Among the challenges of micro/nano manipulation, a long-standing difficulty is the release of grasped objects from the end effector due to strong adhesion forces. Force scaling causes surface forces (i.e., adhesion forces) including the capillary force, electrostatic force, and van der Waals force to dominate volumetric forces (e.g., gravity). In the pursuit of rapid, accurate release methods, several strategies have thus far been proposed.
Alteration of surface adhesion property between pick and place allows a single needle probe to manipulate micro objects (O. Fuchiwaki, A. Ito, D. Misaki, and H. Aoyama, “Multi-axial micromanipulation organized by veratile micro robots and micro tweezers,” in Proc. IEEE Int. Conf. Robotics Automation, Pasadena, Calif., USA, May 2008, pp. 893-898). This method relies on UV-cured adhesive applied onto a substrate for object release.
Rolling movements of a single needle probe were used to manipulate the adhesional forces between pick and release, and had successfully constructed a diamond-shaped structure using microspheres (S. Saito, H. T. Miyazaki, T. Sato, and K. Takahashi, “Kinematics of mechanical and adhesional micromanipulation under a scanning electron microscope,” J. Appl. Phys., vol. 92, pp. 5140-5149, 2002). The method proposed by Saito et al, however, requires a highly skilled operator to execute complex motions and relies on trial-error processes.
Active release methods that do not rely on substrate adhesion properties for release were also proposed. Electric field created by substrate—probe potential difference was used to detach the object from the probe (K. Takahashi, H. Kajihara, M. Urago, S. Saito, Y. Mochimaru, and T. Onzawa, “Voltage required to detach an adhered particle by coulomb interaction for micromanipulation,” J. Appl. Phys., vol. 90, pp. 432-437, 2001). This method, however, requires the substrate, probe, and object to be electrically conductive.
Vacuum based method creates pressure differences between pick and place (W. Zesch, M. Bmnner, and A. Weber, “Vacuum tool for handling micro objects with a nano robot,” in Proc. IEEE Int. Conf. Robotics Automation, Albuquerque, N. Mex., USA, April 1997, pp. 1761-1766). This method, however, is not suitable for use within a vacuum environment such as inside the SEM (scanning electron microscope), which limits its ability to manipulate sub-micrometer objects.
Micro peltier coolers were used to form ice droplets instantaneously for picking up micro objects, and thawing the ice droplets to release objects (B. López-Walle, M. Gauthier, and N. Chaillet, “Principle of a sub-merged freeze gripper for microassembly,” IEEE Transactions on Robotics, vol. 24, pp. 897-902, 2008). The manipulation disclosed by López-Walle et al, however, must take place in an aqueous environment.
U.S. Pat. No. 6,987,277 discloses a method for pick and place of nano objects by selectively activating spots on a passivated substrate using a scanning probe microscope tip, then release the nano objects onto the activated spots using chemical and physical binding forces. This manipulation process requires specially treated sample and substrate.
U.S. Pat. No. 6,648,389 discloses a vibration-based release microgripper for pick and release. The fabrication process of the microgripper limits its scaling down capability, and the release accuracy is poor, as described in a similar, vibration-based design (Y. Fang and X. Tan, “A dynamic jkr model with application to vibration release in micromanipulation,” in Proc. IEEE/RSJ Int. Conf. Intelligent Robots and Systems, Beijing, China, October 2006, pp. 1341-1345).
U.S. Pat. No. 7,025,619 discloses the use of mechanical sockets for locking two micro components together for assembly. This method requires each component to have a specially designed mechanical junction for assembly.
While several patented microgripper designs exist, they only focus on the grasping capability. There are no known gripper designs that are capable of reliable release. For example, U.S. Pat. No. 6,862,921 (Veeco Instruments Inc.) discloses the use of two scanning probe microscope tips that are used in combination to form tweezers for manipulation; U.S. Pat. No. 7,261,352 (Samsung Electronic Co., Ltd) discloses a carbon nanotube gripping device. Other companies that specialize in micro and nanotechnologies, such as Zyvex or Nascatec, have commercialized different types of microgrippers and probes capable of picking up objects, but all lack release mechanisms.
Besides the lack of release capabilities in existing designs, existing designs also have limited down scaling capabilities. To manipulate nanometer-sized objects, the manipulation tip of the device ideally should have a comparable size to the object. This is difficult to accomplish in most fabrication processes for MEMS-based (microelectromechanical systems) microgrippers, where all structural features in the device typically have the same thickness. By reducing the device thickness, the performance of the microactuator is greatly reduced due to decreased overlapping areas or volume; and the poor aspect ratio in flexures produces undesired motions during operation. While down scaling is easy to achieve with a needle probe, the pick-up capability of needle probes is very limited.
In summary, the lack of highly repeatable and accurate release methods limits efficient, automated micro and nano manipulation, which is important for in situ sample preparation and handling as well as for the construction of micro and nano structures/devices. What is needed is a gripper design that permits (1) easy, secured grasping of micro, nanometer-sized objects; (2) rapid, highly reproducible, accurate release of the objects; and (3) ready down scaling for manipulating sub-micrometer and nanometer sized objects.